With the increasing shortage of water resources and increasing standards of energy conservation and emission reduction, accurate water metering and efficient management of systems for water supply have become one of the urgent tasks of current water industry. According to statistics, the average losses in water from leakage of general cities are around 20% to 30%, which is a great loss in resource and energy. To minimize this loss, flow meters should be installed in water supply pipelines to monitor the flow rate and pressure of pipe networks live. However, most pipe networks have been laid and run for many years. It requires cutting off water supply and cutting existing pipelines to install flow cell type flow meters or water meters, also with higher project costs. So flow cell type flow meters or water meters have their limitations in practical applications.
In recent years, DMA, District Metering Areas, method has been receiving attentions in urban water leak detections. However, in practical, it is found that the costs of flow cell type flow meters or water meters increase rapidly as the pipe sizes increase, which leads to a decrease in the amount of meters installed by urban water supply companies. This increases the areas of districts for leak detection, which also decreases the efficiency and accuracy of leak detection.
Insertion type ultrasonic flow meter does not require cutting pipelines or cutting off water supply and can be installed hot fast and easily. Moreover, the cost does not change a lot with pipe size. Therefore getting wide attentions.
The main types of existing insertion type flow meters are mechanical, electromagnetic and ultrasonic. Insertion type mechanical flow meters are traditional mechanical flow instruments, e.g. propeller flow meter, turbine flow meter, etc., inserted and installed inside pipeline. This type of flow meter has the common weaknesses of mechanical flow meter, which is easy to wear, blocked or jammed, high starting flow, low accuracy, etc. Thus there are many limitations in practical applications making it difficult to take accurate measurement or to detect leakage in pipe network.
Insertion type electromagnetic flow meter has the advantages of no moving part, low maintenance cost and battery powered. However, because it can be easily affected by electromagnetic environment and fluid conductivity, in addition to its bad performance at low flow velocity and high cost, it is not widely used.
Insertion type ultrasonic flow meter has the advantages of no moving part and low maintenance cost. It usually uses a pair of transducers, which are installed on both sides of the pipe, face-to-face, or on the same side of the pipe with a certain distance from each other. The transducers are usually flush with or near the inner wall of the pipe. So, during measurement, the signals need to travel a long distance, such as once or twice the pipe diameter, causing a large sound attenuation. This requires stronger transmit power, more complex weak signal detection and processing calculations. So the system power consumption is generally too high to be powered by battery. Because there is usually no external power available at the locations in urban pipeline where flow meters need to be installed, it is not practical to use meters without battery power.
Moreover, due to the strong noise in received signal, it is difficult for insertion type ultrasonic flow meter to measure low flow velocity, making leak detection impossible.
Furthermore, during the installation process, the relative distance of the sensor needs to be adjusted according to the actual situation in order to achieve the best received signal strength. Therefore, the system zero cannot be accurately defined, affecting the measurement results.
In summary, there is currently not a better flow meter can be installed easily and work reliably, has a low maintenance cost and reasonable price, meanwhile can be powered by battery and measure low flow velocity. Especially the latter two are very important for practical applications. Because most of the water pipelines are unable or not easy to get the urban power, power supply of flow meter is a very important issue. On the other hand, water leakages are slow leaks with a low flow velocity at early stages. But because the large diameter of pipe network, the amount of water leakage is not small. Thus, the low flow velocity performance of flow meter is very important to water leakage detection.